Toxicology (from the Greekwords toxicos and logos) is the study of the adverse effects of chemicalson living organisms . It is the study of symptoms, mechanisms, treatments and detection of poisoning, especially the poisoning of people.

What is Toxicology?

Toxicology is the study of the adverse effects of chemicals on living systems, whether they be human, animal, plant or microbe. ‘Adverse effect’ can range from a life threatening injury to something that might be considered a minor annoyance. A mild irritant that causes watering of the eyes may not seem like a significant or real adverse effect, but for the person operating fine equipment, such effect can be not only deleterious but potentially dangerous.

Toxicology is an inter-disciplinary science that integrates the principles and methods of many fields: chemistry, biology, pharmacology, molecular biology, physiology and medicine. For example, by combining the study of the physiological effects of certain chemical structures and the molecular biological mechanisms that explain those effects, the toxicology can provide better understanding of the actions of a class of chemical substances, a finding of value to the chemist.

Pharmacodynamics

Pharmacodynamics is the study of the biochemical and physiological effects of drugs and the mechanisms of drug action and the relationship between drug concentration and effect. It is often summarily stated that pharmacodynamics is the study of what a drugdoes to the body, whereas pharmacokineticsis the study of what the body does to a drug.

Drug action

Desired activity

The desired activity of a drug is mainly due to one of the following:

• Cellular membranedisruption
• Chemical reaction
• Interaction with enzymeproteins
• Interaction with structuralproteins
• Interaction with carrierproteins
• Interaction with ion channels
• Ligand bindingto receptors:
  • Hormonereceptors
  • Neuromodulatorreceptors
  • Neurotransmitterreceptors

General anestheticswere once thought to work by disordering the neural membranes, thereby altering the Na⁺ influx. Antacidsand chelating agentscombine chemically in the body. Enzyme-substrate binding is a way to alter the production or metabolism of key endogenouschemicals, for example aspirinirreversibly inhibits the enzyme prostaglandin synthetase (cyclooxygenase)thereby preventing inflammatoryresponse. Colchicine, a drug for gout, interferes with the function of the structural protein tubulin, while Digitalis, a drug still used in heart failure, inhibits the activity of the carrier molecule, Na-K-ATPase pump. The widest class of drugs act as ligands which bind to receptors which determine cellular effects. Upon drug binding, receptors can elicit their normal action (agonist), blocked action (antagonist), or even action opposite to normal (inverse agonist).

In principle, a pharmacologist would aim for a certain plasmaconcentration of the drug for a desired level of response. In reality, there are many factors affecting this goal. Pharmacokinetic factors determine peak concentrations, and levels cannot be maintained with absolute consistency because of metabolic breakdown and excretory clearance. Geneticfactors may exist which would alter metabolism or drug action itself, and a patient's immediate status may also affect indicated dosage.

Undesirable effects

Undesirable effects of a drug include:

• Increased probability of cell mutation(carcinogenicactivity
• A multitude of simultaneous assorted actions which may be deleterious
• Interaction (additive, multiplicative, or metabolic)
• Induced physiological damage, or abnormal chronic conditions

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